Drive system and vehicle for use therewith

ABSTRACT

An electrical drive system is controlled by a microprocessor-based, electronic control unit which is coupled to operator-generated input signals and various feedback signals to individually control the major components of the drive system including a turbine engine, a three-phase alternator, power control units and their respective synchronous AC motors and gearboxes. A combat vehicle which utilizes the drive system includes a vehicle bed on which right and left sets of three wheels are mounted on opposite sides of the centerline of the vehicle in driving engagement with their respective gearboxes. Each of the wheels includes a hollow hub in which its gearbox and its synchronous AC motor is mounted. A torsilastic suspension system supports the wheels on the vehicle bed. The turbine engine drives the alternator which comprises a brushless, synchronous device having a variable three-phase power output. Each of the power control units first rectifies the three-phase output power, then controls the resulting DC power and finally converts the controlled DC power to variable frequency AC power to independently control the speed and torque of its motor. The vehicle turns by electrically slowing the motors on one side of the centerline of the vehicle and electrically speeding up the motors on the other side so that the vehicle turns about the wheels whose motors are electrically slowed (i.e. regenerative skid steering).

TECHNICAL FIELD

This invention relates to electrical drive systems and vehicles for usetherewith and, in particular, to electrical drive systems and vehiclesfor use therewith wherein the various components of the drive system arecontrolled from an electronic control unit responsive tooperator-generated input signals and feedback signals indicating thecondition of the various components of the drive system.

BACKGROUND OF THE INVENTION

The U.S. military has a continuing interest in wheeled armored vehicles.A comparison of wheeled and tracked vehicles reveals a major differencein silhouettes. As can be readily appreciated, a low silhouette offersmany advantages in combat. The major contributing factors to thisdifference in silhouette are the automotive-type drive train andsteering mechanisms used in conventional wheeled armored vehicles.Hydraulic and electrical drive systems potentially allow configurationscompetitive with silhouettes of tracked vehicles.

To achieve this advantage of a hydraulic or electrical drive system, thewheel drive motor should be located as near as possible to the wheels.In the case of hydraulic drive systems, this requires much piping,hydraulic rotating joints, and complex road arms. Steering wheels becomea very difficult hydraulic problem. A speed range of 3 to 60 mph isdifficult to achieve when 60% grade torque is required at the low endand highway conditions at the upper end. The components become verylarge and efficiency is low. Weight of pumps, fluids, control valves,piping and cooling also appears to be excessive. Controls for a 6×6hydraulic system are quite involved. Cold weather (-45° F.) start up ofa hydraulic system is time consuming. Reaction time to full power fromidle is not fast. Momentary overloads, as might be required for evasiveaction, are not available with hydraulics because of pressurelimitations. Consequently, there appears to be little advantage inpursuing the hydraulics drive train approach for a modern combatvehicle.

The state of the art in electric motors and their controls reveals amaturing technology in speed and torque control. There are a widevariety of types of electric drive motors, each with its own advantagesand disadvantages. One of the most common types of drive motors is astepper motor. This motor provides open loop position and velocitycontrol. They are relatively low in cost and they interface easily withelectronic drive circuits. Recent developments in control systems havepermitted each stepper motor "step" to be divided into many incrementalmicrosteps. As many as 10,000 or more microsteps per revolution can beobtained. Motor magnetic stiffness, however, is lower at thesemicrostepping positions. Typically, stepper motors are run in an openloop configuration. In this mode they are underdamped systems and areprone to vibration, which can be damped either mechanically or throughapplication of closed loop control algorithms. Power-to-weight ratiosare lower for stepper motors than for other types of electric motors.

The permanent-magnet, direct-current, brush-commutated motor is widelyavailable and comes in many different types and configurations. Thelowest-cost permanent magnet motors are the ceramic (ferrite) magnetmotors. Motors with alnico magnets have a higher energy product andproduce higher motor constants than equivalent sized motors with ceramicmagnets. (Motor constant is defined as torque produced divided by thesquare root of power consumed.) Rare-earth (samarium-cobalt) motors havethe highest energy product magnets, and, in general, produce the largestpeak torques because they can accept large currents withoutdemagnetizing. However, these larger currents cause increased brush wearand more rapid motor heating.

Another subset of DC permanent-magnet brush motors are ironless rotormotors. Typicallly, these motors have rotors made of copper conductorsenclosed in epoxy glass cup or disk rotor structures. The advantages ofthese motors include low inertia and negligible inductance, whichreduces arcing, extends brush life, and results in short electrical andmechanical time constants. Because these motors have no iron in therotor they have very little residual magnetism and consequently very lowcogging torques. Disk-type motors have several advantages. They haveshort overall lengths, and because their rotors have many commutationsegments they produce a smooth output with low torque ripple. Adisadvantage of ironless armature motors is that they have a low thermalcapacity due to low mass and limited thermal paths to their case. As aresult, they have rigid duty cycle limitations or require forced-aircooling when driven at high-torque levels.

The weakest links in most motor designs are the bearings and brushes.Brushless DC motors, also classified as synchronous AC motors, have beendeveloped. They substitute magnetic and optical switches and sensors ndelectronic switching circuitry for the graphite brushes and copper barcommutators, thus eliminating the friction, sparking, and wear ofcommutating parts. Brushless DC motors generally have good performanceat low cost because of the decreased complexity of the motor. However,the controllers for these motors are generally more expensive becausethey must include all of the switching circuitry. The cost, reliabilityand flexibility of such controllers, however, have also improved due tosuch features as improved semiconductor technology and the use ofmicroprocessor control technology.

Brushless DC motors also have increased reliability and improved thermalcapacity. This improved thermal capacity occurs because in brushlessmotors the rotor is a passive magnet and the wire windings are in thestator, giving them good thermal conductivity to the motor case.

The U.S. Pat. No. to Fengler 4,211,930 discloses a constant-speed,continuously-running, low-power diesel engine or turbine which drives afixed-frequency, two-pase alternator, the output from which, for directdrive, flows to the stator pole piece windings of fourindependently-rotating stepping motors operating synchronously with theDC alternator. Each motor also includes a rotor having a plurality ofcircumferentially spaced, rare-earth magnets of alternating polarity.Each stepping motor is connected to its respective traction wheel of amotor vehicle, thereby propelled at a limited maximum speed sufficientto overcome normal wind resistance over a level road. The motors areconnected to a suspension arm assembly and swivel around a hinge line atthe center of the vehicle. In starting, during acceleration, and forpropulsion at higher speeds, direct current from a storage battery iscaused to pulsate and is added to the current from the alternator to thestepping motors. A solid state control circuit selectively controls thefrequency of a variable frequency generator electrically connected tothe pulse-responsive electrical power system to vary the frequency ofthe current supplied to the stepping motors and thus vary the vehiclespeed. The frequency and phase of the stator currents are controlledthrough SCR's or thyristors to maintain the magnetic field and themaximum torque condition, independent of rotor speed or supplyfrequency. During idling, the alternating current from the alternator isrectified and recharges the battery. During braking, the consequentdriving of the stepping motors causes them to generate alternatingcurrent which is rectified and returned to the battery. By varying thefrequencies of the current delivered to the right side motors ascompared with those delivered to the left side motors and vice versa, inresponse to the turning of the steering wheel in rounding a curve in theroad, a differential action is obtained.

The U.S. Pat. No. to Ehrenberg 4,089,384 discloses a vehicle including aturbine-drive electric generator, and a plurality of independentmotor-wheel systems. The AC voltage from the generator is rectified andthe resulting DC voltage is supplied to the serially connected DCmotors.

The U.S. Pat. No. to Kassekert et al 3,915,251 discloses an electricvehicle drive having a DC drive motor with shunt field control. A DCpower supply is connected to the drive motor. Drive pulleys and beltstransfer drive torque from the motor to the drive wheels.

The U.S. Pat. No. to Etienne 4,187,436 discloses an electric hybridvehicle including driving wheels driven by an electric driving motorsupplied with current by a battery. The battery is charged by analternator which, in turn, is driven by an engine. The excitationwinding of the alternator is controlled by a circuit which, in turn, iscontrolled by a circuit which monitors the state of the battery. Logiccircuitry is also provided for controlling the engine.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an electrical drivesystem that offers the reliability and ruggedness required of a militaryvehicle but still yields the small size and light weight needed tocreate a vehicle with a lower silhouette and increased agility.

Another object of the present invention is to provide a combat vehicleincluding an electrical drive system that is compatible with futureelectrical weapons systems.

Yet still another object of the present invention is to provide avehicle including an electrical drive system that is reliable andrelatively easy to maintain.

In carrying out the above objects and other objects of the presentinvention there is provided a drive system for use in a vehicle havingleft and right sets of wheels mounted on opposite sides of thecenterline of the vehicle and adapted to be electrically driven from asource of mechanical power. Each of the wheels includes a hollow hub.The drive system includes left and right sets of wheel drive units. Eachof the wheel drive units is connected within its respective hub forrotation of its respective wheel upon the application of drive torque.The system also includes left and right sets of electric drive motors.Each of said motors is connected to its respective drive unit within itsrespective hub for receiving electrical power and converting theelectrical power into drive torque. An alternator is connected to thesource of mechanical power for receiving the application of drive torquetherefrom and converting the mechanical power into electrical power.Power control means is coupled to the alternator means and each of themotors. The power control means conditions and controls the electricalpower received by each of the motors to independently control the speedand torque of each of the motors.

Further, in carrying out the above objects and other objects of thepresent invention, the above-noted drive system is supported on avehicle bed by a suspension system.

Preferably, the alternator, the power control means, the drive units andthe source of mechanical power are centrally controlled by an electroniccontrol unit responsive to operator-generated input signals and tofeedback signals from the alternator, the power control means and eachof the motors.

The drive system and vehicle for use therewith as constructed above hasnumerous advantages. For example, the electrical drive system offers thereliability and ruggedness required of a military vehicle and stillyields the small size and light weight needed to create a vehicle with alower silhouette and increased agility. Also, the electrical drivesystem provides a ready source of electrical power for future weaponsystems. The use of an electronic control unit provides the necessarycontrol for a responsive drive system of the sophistication needed forincreased vehicle control, mobility and agility. Also, such anelectronic control unit allows the use of electronic braking,regenerative skid steering, cruise control, anti-skid and faultdiagnostics.

The objects, features and advantages of the present invention arereadily apparent from the following detailed description of the bestmode for carrying out the invention when taken in connection with theaccompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of a vehicle test bed, including anelectrical drive system, constructed in accordance with the presentinvention;

FIG. 2 is a side view of the vehicle test bed with many componentsthereof indicated by phantom lines;

FIG. 3 is a top view of the vehicle test bed illustrating, by phantomlines, the layout of the various components of the drive system andtheir relationship with other components of the vehicle;

FIG. 4 is a view, partially broken away and in cross section,illustrating a gearbox and its associated electric motor positionedwithin the hub of a wheel of the vehicle and its related suspensionunit;

FIG. 5 is a view, partially broken away and in cross-section,illustrating an electric motor for use in the drive system;

FIG. 6 is a schematic view of the various components of the vehicledrive system and the flow of power therebetween; and

FIG. 7 is a schematic view of a microprocessor-based, electronic controlunit, the various inputs and outputs thereof and the flow of control andfeedback signals therebetween.

BEST MODE FOR CARRYING OUT THE INVENTION

Referring now to FIGS. 1 through 3, there is illustrated an armor-platedvehicle, including an electrical drive system, constructed in accordancewith the present invention. While illustrated as a vehicle with sixwheels, the vehicle, collectively indicated at 10, could also be avehicle having tracks or a different number of wheels.

While illustrative only, the vehicle 10 is approximately 18 feet long,10 feet wide and five feet high, thereby providing a relatively lowprofile or silhouette. Also, because the vehicle 10 is electricallydriven as described hereinbelow, there is sufficient on-board electricalpower to handle future electrical weapon systems, for example, on thetop surface of a vehicle bed 12 of the vehicle 10.

One or more operators are capable of being seated in a cockpit area 14.Within the cockpit area 14 there are provided manual speed, steering andbrake controls as well as an engine switch. These operator controls arepreferably capable of generating analog electrical signals which areprocessed by an electronic control unit, generally indicated at 16, alsolocated in the cockpit area 14. In general, the electronic control unit16, as will be described in greater detail hereinbelow, controls many ofthe components of the drive system. The control unit 16 also displays avariety of operator information on a monitor/display 18, also within thecockpit area 14.

The vehicle 10 has left and right sets of wheels, generally indicated at20, supported on opposite sides of a centerline 21 of the vehicle bed12. As best shown in FIG. 4, each wheel includes a hollow hub, generallyindicated at 22. A tire, illustrated by phantom lines at 24, is mountedon a rim 26 of each wheel 20. In turn, each rim 26 is fixedly mounted bybolt and nut assemblies 28 to outer wheel housing members 30 and 32 ofthe hub 22. The housing members 30 and 32 rotate together with itsrespective tire 24.

The housing members 30 and 32 of each hub 22 rotate relative to andsupport their respective motor housing 34 by means of bearings 36. Inturn, each motor housing 34 supports a synchronous AC motor, generallyindicated at 38. An output shaft 39 of each synchronous AC motor 38 isin driving engagement with a two-speed gearbox, generally indicated at40. Each gearbox 40 includes a shiftbox 42 which is controlled by theelectronic control unit 16 to drive its hub 22 from either a high speedgear 44 or a low speed gear 46.

Referring to FIG. 5, each of the motors 38 includes a three-phase,oil-cooled stator or stator assembly 48 and a rotor or rotor assembly,generally indicated at 50. Preferably, the rotor 50 has a multiplicityof rare earth permnent magnets 52 circumferentially arranged andsupported between the output shaft 39 and a support sleeve 54.

Referring again to FIG. 4, each wheel 20 includes a brake assembly,generally indicated at 56. Each brake assembly 56 includes an annularbraking member 58 which is fixedly secured to the second housing member32 such as by a plurality of bolts 60. Each brake assembly 56 alsoincludes a hydraulically actuated braking device 62 which selectivelyengages brake pads 64 of the braking member 58 upon the generation of abrake signal by the operator of the vehicle 10. The braking device 62 isfixedly secured to the motor housing 34, such as by bolts (not shown).

A torsilastic suspension system supports the wheels 20 on the vehiclebed 12. In particular, the suspension system includes suspension units,generally indicated at 66, for each of the wheels 20. Each suspensionunit 66 includes a road arm 68 fixedly connected at one end thereof toits motor housing 34 by bolts (not shown). The opposite end of each roadarm 68 is conventionally mounted about a rubber element 70 of itssuspension unit 66. Each tubular element 70, in turn, is fixedly mountedto a portion 72 of the vehicle bed 12. In general, the torsilasticsuspension system operates in a conventional fashion to support thewheels 20 on the vehicle bed 12.

As best shown in FIG. 2, the suspension system also includes shockabsorbers 73 for each of the wheels 20. One end of each shock absorber73 is pivotally connected to the vehicle bed 12 and its opposite end ispivotally connected to its respective road arm 68.

The vehicle 10 is driven from a source of mechanical power, preferablycomprising a turbine engine 74 mounted on the vehicle bed 12. An on/offswitch 76, as illustrated in FIG. 7, is located on an operator controlpanel within the cockpit 14 and is coupled on line 77 to the controlunit 16 which, in turn, alternately stops or starts the engine 74.Preferably, the switch 76 is provided as a closed, isolated relaycontact to the electronic control unit 16. Another input to the controlunit 16 may indicate that the engine 74 is at or above its minimumoperational speed and is available for load application.

The vehicle 10 also includes a brushless, synchronous alternator 78which is mounted on the vehicle bed 12 and is in driving engagement withthe turbine engine 74 through a gearbox 79. Preferably, the alternator78 comprises a brushless, three-phase, synchronous machine having arotating rectifier main exciter and a self-contained permanent magnetexciter for regulator power supply. Also, preferably, the alternatorspeed at engine idle is approximately 2,800 rpm and alternator speed atrated engine power is approximately 9,000 rpm. 2,800 rpm represents theminimum operational speed at which the maximum load does not exceed 100shaft hp. Preferably, the alternator 78 is lubricated by the flow ofpressurized oil and is cooled by a fan internal to the alternator 78.

The alternator 78 provides a three-phase, power output to shielded powerleads 80. The power leads 80 are coupled to a power control means orcircuit, generally indicated at 81, for conditioning and controlling theelectrical power delivered to each of the motors 38. The power controlcircuit 81 includes power control units, generally indicated at 82, foreach of the motors 38. Each power control unit 82 independently controlsthe speed and torque of its motor 38. Preferably, each of the powercontrol units 82 is oil-cooled and is what is commonly known as a DClink converter. However, it is to be understood that other types ofpower control units could be provided.

Each power control unit 82 preferably includes a three-phase rectifiercircuit 84 for converting the three-phase AC power from the alternator78 to DC power. The DC power is then coupled to a control circuit 86which is responsive to a set of control signals from the electroniccontrol unit 16 on line 85 for individually controlling the DC powerand, in particular, the DC current and the DC voltage. Finally, thecontrolled DC power is coupled to an inverter circuit 88 which isresponsive to a second set of control signals appearing on line 87 fromthe electronic control unit 16. The inverter circuit 88 converts thecontrolled DC power from the control circuit 86 to a variable frequency,AC power. In turn, the AC power is coupled to the stator 48 of itsrespective motor 38 on output leads 90.

Referring again to FIG. 7, operator-generated speed commands (i.e.forward, neutral and reverse) appear on line 92 to provide an analogelectrical signal appearing on line 94. Similarly, anoperator-generated, steering command signal appears on line 96 and isconverted into a corresponding analog electrical signal appearing online 98. Likewise, an operator-generated brake command signal appears online 100 and is converted to an analog electrical signal appearing online 102.

Each of the signals appearing on the lines 94, 98 and 102 are convertedto a digital representation by an analog-to-digital and buffer circuit104 of the electronic control unit 16. In turn, the correspondingdigitized signls appear on line 106 and are fed into a microcomputer,generally indicated at 108, of the electronic control unit 16.Preferably, the microcomputer 108 includes a clock 110, a memory circuit112 having a volatile RAM and a non-volatile ROM, a CPU 114 and inputand output circuitry 116 which are all interconnected and controlled ina conventional fashion. While illustrated as a microcomputer 108, it isto be understand that other types of control logic could be providedwithin the electronic control unit 16.

The electronic control unit 16 further includes a digital-to-analog andan analog-to-digital circuit 118 which interfaces the microcomputer 108along bi-synchronous link 120 to the engine 74, the three-phasealternator 78, each of the power control units 82 and their respectivemotors 38 and wheel drive units 40. For example, the circuit 118provides throttle and on-off control signals to the turbine engine 74.Also, the circuit 118 provides an excitation (EFA) control signal to thealternator 78 and receives a speed/voltage feedback signal from thealternator 78. Likewise, the circuit 118 receives voltage and currentfeedback signals from each of the power control units 82 on line 122which the microcomputer 108 uses to control each of the power controlunits 82 in accordance with ciontrol algorithms, shaping algorithms,event algorithms and monitor and diagnostic algorithms provided as itscontrol logic. In this way, the microcomputer 108 can accept variousoperator-generated input signals and feedback signals and outputappropriate control signals to the various components of the vehicledrive system.

In similar fashion, speed feedback signals from each of the motors 38are fed into the circuit 118 along line 124. Depending on the speed ofeach of the motors 38 and the control algorithms within themicrocomputer 108, a low/high gear control signal is fed to each of thewheel drive units 40 on line 126 to selectively shift the wheel driveunits 40 between high and low speed.

In summary, the electronic control unit 16 generates control and speedsignals for each of the power control units 82, each of the wheel driveunits 40, the alternator 78 and the turbine engine 74. In general, thesesignals are in response to operator-generated throttle, brake andsteering commands, various feedback signals from the various componentsof the drive system and operator-selected mode signals (i.e. forward,reverse, neutral, pivot, etc.). The main functions performed by theelectronic control unit 16 are (1) engine speed and alternatorregulation to minimize fuel consumption; (2) individual invertervoltage/frequency control; (3) individual wheel spin/slide control; (4)power parameter limiting; (5) status/fault annunciation; (6)implementation of steering commands; (7) implementation of brakingcommands; and (8) electronic braking control (both dynamic andregenerative).

For example, regenerative skid steering is provided when each of thepower control units 82 receives control signals from the electroniccontrol unit 16 so that the motors 38 on one side of the vehicle 10 areslowed and the motors 38 on the other side of the vehicle are sped up.The motors 38 on the one side of the vehicle 10 slow the rotation oftheir respective wheels and thereby these motors 38 generate electricalpower. The motors 38 on the other side of the vehicle 10 increase therotation of their respective wheels 20 as these motors 38 are drivenwith increased electric power.

The advantages accruing to a drive system and a vehicle for usetherewith as constructed above are numerous. For example, the electricaldrive system provides a ready source of electrical power for futureelectrical weapon systems. Also, the use of an electronic control unitprovides the necessary control for a responsive drive system of thesophistication needed for increased vehicle control, mobility andagility. Also, the electronic control unit allows the use of electronicbraking, regenerative skid steering, cruise control, anti-skid and faultdiagnostics.

The electrical drive system offers the reliability and ruggednessrequired of a military vehicle yet still yields the small size and lightweight needed to create a vehicle with a low silhouette and increasedagility.

While the best mode for carrying out the invention has herein beendescribed in detail, those familiar with the art to which this inventionrelates will recognize various alternative designs and embodiments forcarrying out the invention as defined by the following claims.

What is claimed is:
 1. A vehicle bed comprising:a vehicle bed; right andleft sets of wheels mounted on opposite sides of the centerline of thevehicle, each of said wheels including a hollow hub; a source ofmechanical power mounted on the vehicle bed; a suspension system forsupporting the wheels on the vehicle bed; right and left sets of wheeldrive units, each of said wheel drive units being connected within itsrespective hub for rotation of its respective wheel upon the applicationof drive torque; right and left sets of electric drive motors, each ofsaid motors being connected to its respective drive unit within itsrespective hub for receiving electrical power and converting theelectrical power into drive torque; an alternator mounted on the vehiclebed and connected to the source of mechanical power for receiving theapplication of drive torque therefrom and converting the mechanicalpower into electrical power; and power control means mounted on thevehicle bed and coupled to the alternator and each of the motors,wherein said power control means conditions and controls the electricalpower received by each of the motors to independently control the speedand torque of each of the motors wherein said power control means isresponsive to power control signals to control the motors to provideregenerative skid steering, one of the sets of motors slowing rotationof its respective set of wheels, the one set of motors generatingelectric power, and the other set of motors increasing rotation of itsrespective set of wheels, the other set of motors being driven withincreased electric power.
 2. The invention as claimed in claim 1 whereinsaid alternator is a brushless, synchronous device responsive to a setof alternator control signals and having a variable three-phase poweroutput.
 3. The invention as claimed in claim 2 wherein each of saidmotors is a synchronous AC motor.
 4. The invention as claimed in claim 3wherein each of said motors has a three-phase stator and a rotor with amultiplicity of permanent magnets.
 5. The invention as claimed in claim4 wherein said magnets are rare earth permanent magnets.
 6. Theinvention as claimed in claim 3 wherein said power control meansincludes a power control unit for each of said motors, and wherein eachof said power control units includes a three-phase rectifier circuit forconverting the three-phase AC power from the alternator to DC power. 7.The invention as claimed in claim 6 wherein each of said power controlunits includes a control circuit responsive to a first set of powercontrol signals for controlling its respective DC power.
 8. Theinvention as claimed in claim 7 wherein each of said power control unitsincludes an inverter circuit responsive to a second set of controlsignals for converting the controlled DC power to AC power, said ACpower being coupled to its respective motor to control its torque andspeed.
 9. The invention as claimed in claim 1 wherein the vehicle has afirst set of three wheels mounted at spaced locations on one side of thecenterline and a second set of three wheels mounted on the opposite sideof the centerline.
 10. The invention as claimed in claim 1 wherein eachof said drive units includes a variable speed gearbox mounted within itsrespective hub, each gearbox being responsive to a set of drive controlsignals to control its speed and wherein each of said drive motorsincludes an output shaft coupled to its respective gearbox within itsrespective hub to transfer drive torque thereto.
 11. The invention asclaimed in claim 10 wherein each of said gearboxes is a two-speedgearbox.
 12. The invention as claimed in claim 1 wherein the source ofmechanical power is a turbine engine and wherein said turbine isresponsive to a set of engine control signals.
 13. The invention asclaimed in claim 12 including gearing for coupling the turbine engine tothe alternator.
 14. The invention as claimed in claim 1 wherein thevehicle is an electrically driven combat vehicle.
 15. An electricallydriven combat vehicle comprising:a vehicle bed; right and left sets ofthree wheels, the sets being mounted on opposite sides of the centerlineof the vehicle, each of said wheels including a hollow hub; a source ofmechanical power including a turbine engine mounted on the vehicle bed;a suspension system for supporting the wheels on the vehicle bed; rightand left sets of three drive units, each of said drive units including agearbox connected within its respective hub for rotation of itsrespective wheel upon the application of drive torque; right and leftsets of three synchronous AC motors, each of said motors being connectedto its respective gearbox within its respective hub, each of said motorshaving a three-phase stator and a rotor with a multiplicity ofrare-earth permanent magnets; a brushless, synchronous alternatormounted on the vehicle bed and connected to the turbine engine forreceiving the application of drive torque therefrom and converting themechanical power into a variable, three-phase output power; and powercontrol means mounted on the vehicle bed and coupled to the alternatorand each of the motors, wherein said power control means conditions andcontrols the electrical power received by each of the motors toindependently control the speed and torque of each of the motors andwherein said power control means controls one set of the motors so thatthe one set of motors slows rotation of its respective set of wheels,the one set of motors generating electric power, and the other set ofmotors increasing rotation of its respective set of wheels, the otherset of motors being driven with increased electric power to therebyprovide regenerative skid steering.
 16. The invention as claimed claim 1or claim 15 wherein the source of power, the alternator, the powercontrol means and each of the drive units are responsive to controlsignals and wherein the invention further comprises an electroniccontrol unit responsive to operator-generated input signals and feedbacksignls from the alternator, the power control means and each of themotors for providing said control signals.
 17. The invention as claimedin claim 1 or claim 15 wherein said suspension system includes asuspension unit for each of said wheels and wherein each of saidsuspension units has a road arm and a torsilastic spring connected toits respective road arm.
 18. The invention as claimed in claim 17wherein said suspension system further includes a shock absorberconnected to each of said road arms.